Network Working Group P. Ashwood-Smih
Internet Draft A. Paraschiv
Expiration Date: February 2002 Nortel Networks
August 2001
MPLS LDP Query Message Description
draft-ietf-mpls-lsp-query-03.txt
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. Internet-Drafts are working
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Abstract
This document describes the encoding and procedures for three new LDP
messages, the Query Message and Query-Reply Message and Partial
Query-Reply Message (the last one is almost identical to the Query-
Reply message; therefore all references to the Query-Reply messages
imply the Partial Query-Reply messages as well, unless otherwise
specified). An LER sends a Query message when it needs to find out
information about an LSP. The Query message is sent for an
established LSP. The Query message can be used for LDP LSPs as well
as for CR-LSPs. The queried data is encoded into the Query-Reply
messages.
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Contents
1 Introduction ............................................. 3
2 Overview ................................................. 3
2.1 LDP Overview ............................................. 3
2.2 CR-LDP Overview .......................................... 4
3 LDP Message Structure Overview ........................... 4
4 Behavior of LSRs with constraints in handling the query messages 5
4.1 LSR does not support the query messages .................. 6
4.2 LSR cannot share any information ......................... 6
4.3 LSR cannot share some of the queried information ........ 6
4.4 LSR can share the queried information ................... 7
5 Query Message ............................................ 7
5.1 Query Message encoding ................................ 8
5.2 Query Message Procedures ................................. 9
6 Reply Messages .......................................... 10
6.1 Query-Reply Message encoding .......................... 11
6.2 Query-Reply Message Procedures ........................... 13
6.3 Partial Query-Reply Message encoding .................. 13
6.4 Partial Query-Reply Message Procedures ................... 14
7 Query TLVs ............................................... 14
7.1 Query Label TLV .......................................... 15
7.2 Query Merge Flags TLV .................................... 16
7.3 Status code summary ..................................... 16
8 Acknowledgments .......................................... 17
9 References ............................................... 17
10 Author's Addresses ....................................... 18
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Changes from previous version:
o Added clarification on Reply message usage.
o Added clarification on query flags.
o Added clarification on how to handle the Query Message Procedures when PHP in use.
1. Introduction
The original Multiprotocol Label Switching (MPLS) architecture
[MPLS-ARCH] was been defined to support the forwarding of data based
on a label. The MPLS architecture does not assume a single label
distribution protocol. A number of different label distribution
protocols are being standardized. This draft describes the query
mechanism for an LSP or CR-LSP. It specifies procedures and encodings
for the new messages added for the query mechanism. Extensions to
RSVP-TE to provide the same functionality are subject for future
study and will be covered in future draft versions.
The new LDP messages are: Query Message, Query-Reply Message and
Partial Query-Reply Message. The following new TLVs are added to
accommodate the encodings for the new query messages:
- Query TLV
- Query Label TLV
- Query Merge Flags TLV
LDP uses the TCP transport for session, advertisement and
notification messages; i.e., for everything but the UDP-based
discovery mechanism. The messages which are added to support the
query mechanism are sent over TCP as well.
2. Overview
2.1. LDP Overview
Label Distribution Protocol (LDP) defined in [LDP Specification]
contains a set of procedures and messages by which Label Switched
Routers (LSR) establish Label Switch Paths (LSP) through a network by
mapping network layer routing information directly to data-link layer
switched paths. LDP associates a Forwarding Equivalence Class (FEC)
with each LSP it creates. The FEC associated with an LSP specifies
which packets are mapped to that LSP.
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2.2. CR-LDP Overview
As described in [Constraint-Base LSP Setup using LDP], Constraint
Base Routing (CR-LDP) offers the opportunity to extend the
information used to setup paths beyond what is available for the
routing protocol.
3. LDP Message Structure Overview
As described in LDP Specification draft, all LDP messages have the
following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U| Message Type | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| Mandatory Parameters |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| Optional Parameters |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
U bit
Unknown message bit. Upon receipt of an unknown message, if U is
clear (=0), a notification is returned to the message originator;
if U is set (=1), the unknown message is silently ignored.
Message Type
Identifies the type of message
Message Length
Specifies the cumulative length in octets of the Message ID,
Mandatory Parameters, and Optional Parameters.
Message ID
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32-bit value used to identify this message. Used by the sending
LSR to facilitate identifying notification messages that may apply
to this message. An LSR sending a notification message in
response to this message should include this Message Id in the
Status TLV carried by the notification message; see Section
"Notification Message".
Mandatory Parameters
Variable length set of required message parameters. Some messages
have no required parameters.
For messages that have required parameters, the required parameters
MUST appear in the order specified by the individual message
specifications in the sections that follow.
Optional Parameters
Variable length set of optional message parameters. Many messages
have no optional parameters.
For messages that have optional parameters, the optional parameters
may appear in any order.
4. Behavior of LSRs with constraints in handling the query messages
Upon receiving a Query message, an LSR has to behave according to its
configuration constraints in handling the query messages and
returning the queried information. The following cases were
identified:
- the LSR does not support the code to handle the messages
for the query mechanism
- the LSR supports the code to handle the messages for the
query mechanism, but it is configured not to return any data
- the LSR supports the code to handle the messages for the
query mechanism, but it is configured not to return part of
the queried data
- the LSR supports the code to handle the messages for the
query mechanism, and it is configured to return all the data
which is queried.
The draft provides flexibility to handle each of the above cases.
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4.1. LSR does not support the query messages
In this case, the LSR has to behave as if it received an unknown
message type. It has therefore to honor the U bit.
4.2. LSR cannot share any information
In this case, the LSR is able to decode and process the query
messages. However, it is configured to hide all the data. It should
propagate the message after it encodes a zero-length TLV for its hop
in the hop list in the Query message. When Query-Reply message is
received from downstream, the LSR is requested to propagate the reply
message upstream after it encodes the zero-length tlvs for the
queried data. When the ingress receives back the reply, it can
identify which TLVs are empty; it can therefore ignore the zero-
length TLVs and process the rest of the data.
Note: zero-length TLV encoding can be used for all types of queried
information except the merge information. The LSR is requested to
signal the fact that the merging information is private by encoding a
special value in the corresponding merge bits (for more information
on the merge flags values please refer to Query Merge Flags TLV
section).
4.3. LSR cannot share some of the queried information
In this case, the LSR is able to decode and process the query
messages. It has to propagate the query messages. It has to encode
values for the data types that it is willing to return and zero-
length TLVs for values for the data that is hidden.
Note: zero-length TLV encoding can be used for all types of queried
information except the merge information. The LSR is requested to
signal the fact that the merging information is private by encoding a
special value in the corresponding merge bits (for more information
on the merge flags values please refer to Query Merge Flags TLV
section).
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4.4. LSR can share the queried information
This is the normal case for an LSR. In this case, the LSR's behavior
has to follow the query and replies procedures described in the
following sections of the draft.
In order to have consistency among data encoded in the query and
reply messages, each LSR which can propagate the messages has to
encode its information in the query and in the reply messages.
The decision that an LSR can share the queried information has to be
controlled through configuration flags. This way each node along the
path can protect its data if they consider it private.
Note: It would be more efficient to control/restrict the private data
per MPLS cloud (inter MPLS domain) and not per LSR node (inter and
intra MPLS domain). When there are different MPLS clouds which have
nodes belonging to different vendors, the control of the private
information could be restricted to the boundary nodes. Within an MPLS
domain, there should be no restrictions on the queried information.
It would be useful to have some knowledge on which are the nodes on
the boundaries and have only those hiding the queried data. Because
there is no mechanism to identify which are the boundary nodes, this
is subject for future study.
5. Query Message
This sections describes the Query message and its encodings and
procedures. This message is meant to be used to gather information
about an LSP. It can be sent at any time for an established LSP.
The draft currently describes the procedures for the cases when the
Query Message is initiated by the ingress LER. Future versions of
the draft may add the procedures for the query message when issued
from a core LSR or from egress.
The Query Message can be used to gather information about:
- LSRs which form the LSP
- labels along the LSP
- information on what LSRs are merging points along the path
- unused bandwidth (as described in "Improving Topology Data
Base Accuracy with LSP Feedback")
- anything that is needed in the future and can be computed and
encoded in a TLV.
The queried information is encoded in the Query-Reply message which
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is sent back upstream, as a response to the Query message.
5.1. Query Message encoding
The encoding for the Query message is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Query (0x0409) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Query Label TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Query TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Hop Count TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message ID
32-bit value used to identify this message.
Query Label TLV
The label associated to the LSP which is queried. This TLV is a
list of Generalized Label TLVs [OPTICAL reference]. The
Generalized Label TLV provides a more generic encoding for
different types of labels. Most of the time the list has one
element; this is the case when the LSP is not tunneled. For
tunneled LSPs, the Label TLV has more that one element; it has to
behave like a label stack (it contains the previous label and the
tunnel's label). See Section Query Label TLV for more information
on Label TLV encoding.
Query TLV
What to query. See Section Query TLV for encoding.
Hop Count TLV
Specifies the number of LSR hops that can still be traversed
before the message is dropped due to loop detection. It is
initialized to the max value of 255 (or the configured value, if
any). Every LSR that receives the Query Message has to subtract 1
from the Hop Count value. The Query message should be dropped if
the hop count value becomes zero; a Notification signaling Loop
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Detection should be sent in reply to the sender of the message.
See [LDP Specification] for Hop Count TLV encoding.
Optional Parameters
This variable length field contains 0 or more parameters, each
encoded as a TLV.
Optional Parameter Length Value
ER TLV var See CR-LDP
LSPID TLV var See CR-LDP
FEC TLV var See LDP
The ER TLV is a list of hops. It is used when the Query flag Q3 is
set. Every LSR should add its IP address. The address to be added
should be the outgoing interface address. Addresses are organized as
a last-in-fist-out stack (the first address in TLV is considered the
top). By carrying this TLV in the Query Message and preserving this
order for the hops, we allow the possibility to interwork the Query
Message with the RSVP Path message.
FEC TLV is used when PHP is in use, for LDP.
LSPID TLV is used when PHP is in use, for CR-LDP.
For more details on the FEC or LSPID usage, please refer to the Query
Message Procedures below.
5.2. Query Message Procedures
The LER ingress initiates the Query message. It populates the Query
TLV Parameters according to what kind of information it wants to
gather. The query for an LSP is done by its label. The only data that
the Query Message could carry is the list of hops. This way, each
node along the path can have a complete route from source to
destination. This is useful for network management. Please note that
this parameter is optional. If the Query message does not contain the
ER TLV, it should be propagated by LSRs along the path without the ER
TLV.
Upon receiving a Query Message, an LSR decodes the label to identify
which LSP is queried. If it cannot find the LSP which is using the
label, it sends back a Notification message with "No Lsp to query"
status. Otherwise, it checks which is the out label which is bound to
the queried in-label and which is the downstream LSR peer. It
replaces the in-label from Query Label TLV with the out-label used by
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the LSP. It then passes the Query message to the downstream peer.
When the Query message gets to a tunnel, it has to be able to handle
both the previous label and the tunnel's label. The Query Label TLV
behaves like a label stack. The previous label is pushed and the
tunnel label is used. At the end of the tunnel, we need to pop the
stack and start substituting the lower level labels.
Upon receiving the Query message, the egress node has to reply with a
Query Reply Message. The Query-Reply Message contains the Query TLV
which was received in the Query Message. The Query TLV tells the LSRs
along the path which information is being queried and allows
intermediate LSRs to piggy back their own queried information on the
Query reply message.
The initiator of a Query reply might nor receive a response back. In
this case, it is the initiator's responsibility to decide if and when
to retry.
If PHP is in use, the Query Message sent from the PHP to the
destination node needs to carry the FEC (for LDP) or LSPID (for CR-
LDP). This information is required because the label between the PHP
and the destination is a special label and the destination cannot
uniquely identify the queried LSP just by using the label value. If
the PHP does not encode the FEC or the LSPID, the destination node
should reply with a notification message with "Ambiguous label
value".
6. Reply Messages
These messages are propagated upstream. There are two types of reply
messages:
- Query-Reply message (final reply)
- Partial Query-Reply message.
The Reply messages carry the queried information upstream. They are
sent in response to a Query message. The ingress which initiated the
Query message is interested to gather the information from all the
nodes along the queried LSP. However, there are situations in which
the Query message does not reach the end point of the queried LSP. In
these scenarios it would be useful if the ingress LSR gathered at
least some information about the LSRs which are along the path, up to
the one that failed. The Partial Query-Reply message provides this
mechanism. It is recommended to use the Partial Query-Reply messages
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when a Query message fails. If the Reply message is full, TCP will
take care of it by segmenting and re-assembling the message.
Both reply messages are described in the following sections.
6.1. Query-Reply Message encoding
This message is generated by the end point of the LSP. It is
propagated upstream, by each LSR along the path.
The encoding for the Query-Reply message is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Query-Reply (0x0410) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Query TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MessageId TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message ID
32-bit value used to identify this message.
Query TLV
What is to be queried. See Section Query TLV for encoding.
Message Id TLV
The value of this parameter is the message id of the corresponding
Query message.
Optional Parameters
This variable length field contains 0 or more parameters, each
encoded as a TLV. The optional parameters are:
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Optional Parameter Length Value
ER TLV var See CR-LDP
Query Label TLV var See Query Label TLV section
IPV4/6 specified link feedback TLV See Improving Topology ...
Query Merge Flags TLV var See Query Merge Flags TLV
section
For simplicity we reuse here TLV types defined for CR-LDP and LDP.
They are:
- IPV4/6 specified link feedback TLV
- ER TLV
- Generalized Label TLV (used in the Query Label TLV encoding)
- Hop Count TLV.
The IPV4/6 specified link feedback TLV is used when the Q1 flag from
the Query TLV is set. It is used to encode the bandwidth information.
For more information on query flags, Q1, Q2, Q3 and Q6, refer to
Query TLV section.
The ER TLV is a list of hops. It is used when the Query flag Q3 is
set. Every LSR should add its IP address. The address to be added
should be the outgoing interface address. Addresses are organized as
a last-in-fist-out stack (the first address in TLV is considered the
top).
The Query Label TLV is a list of labels. It is used when the Query
flag Q2 is set. It is populated with the labels used for the path
which is queried. For tunneled LSPs, the Query Label TLV represents a
list of labels associated to the lowest level tunnel.
If Q3 and Q2 flags are set, the labels should be encoded in the same
order as the hops.
Query Merge Flags TLV is a list of pairs of bits. It has variable
length and every two bits in the mask will correspond to an LSR along
the path. Its length is rounded up to the next byte. If Q6 is set,
every LSP along the path will have to set its corresponding bits in
the mask. The bits have to be set in the same order as the labels and
hops. Usually, Q6 is set when Q2 set and/or Q3 set.
For more information for the TLV encodings of the TLVs which are
reused, please see CR-LDP draft, LDP draft and IMPROVING TOPOLOGY
DATA BASE ACCURACY WITH LSP FEEDBACK VIA CR_LDP draft.
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6.2. Query-Reply Message Procedures
A Query-Reply message is initiated by an egress node which receives a
Query message, if the egress is able to identify the queried LSP. If
not, the egress replies with a Notification message with "No Lsp to
query" status.
Upon receiving the Query message, the egress node has to reply with a
Query Reply message. The egress node has to encode into the Query-
Reply message a MessageId Tlv. The mapping between a Query and a
Query-Reply Message is done based on the message id. Besides the
MessageId Tlv, the egress has to encode the information that was
queried (bandwidth, path, etc).
After the encoding is done, the query reply message is sent back, on
the reversed path, towards the ingress. Every LSR across the LSP has
to encode its information according to what query flags are set.
6.3. Partial Query-Reply Message encoding
The Partial Query-Reply message is initiated by LSRs along the
queried path. The message is generated only if the following rules
apply:
- if the Query message asked for partial
replies (the Query message signals this request
through Q8 bit)
- if the LSR is configured to provide partial replies.
The encoding for the Partial Query-Reply message is identical to the
Query-Reply, except the message type. For more details on the
encoding please refer to the Query-Reply encoding.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|Partial Query-Reply (0x0411) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Query TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MessageId TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional Parameters |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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6.4. Partial Query-Reply Message Procedures
The procedures are similar to the Query-Reply's procedures. Upon
receiving a Query message, an LSR will check the flag from the Query
message (Q8) which signals if the partial replies are requested by
the ingress node. If the flag is set, the LSR has to check next if it
is configured to fulfill this request. If the LSR supports partial
replies, it has to create a Partial Query-Reply and encode the
queried data and send it upstream like any Query-Reply messages. It
has then to process the Query message according to the Query message
procedures. When an LSR receives a Partial Query-Reply from upstream,
it should encode its information according to what is queried and
propagate the message. It is recommended to use the Partial Query
mechanism when the Query message fails (when the ingress LER does not
receive a Query-Reply message in response to a Query message).
7. Query TLVs
The Query TLV is used to specify the information being queried. The
Query TLV travels in the Query message to the egress node, where it
is copied into a reverse flowing Query-Reply messages and used by the
egress and intermediate LSRs to know what information is being
queried.
The format for the Query TLV is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| Query TLV (0x0840) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Query Flags | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Query Flags can be set according to what the Query is used for.
+--+--+--+--+--+--+--+--+
|Q8|Re|Q6|Re|Re|Q3|Q2|Q1|
+--+--+--+--+--+--+--+--+
They can be:
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- Q1 : query the bandwidth; if set, the LSR that
receives the Query message has to encode the bandwidth
that is available on the link (unused bandwidth);
- Q2 : query the labels which are associated to each hop in the
path;
- Q3 : query the LSRs which form the LSP which is queried;
if set, the LSR that received the Query-Reply message
has to encode the current hop in the ER-TLV
- Q6 : query which LSPs along the path are merging points; if set,
the LSR that receives the Query message has to encode
if it is a merging point; the encoding is done in the
Query Merge flags TLV.
- Q8 : if set, the ingress requests partial query-replies;
each LSR along the path is signaled to send a Partial Query Reply.
7.1. Query Label TLV
The Query Label TLV is used to encode the labels used along the path
which is queried. Note: Query Label TLV is used in both Query and
Query Reply. It is a required parameter in the Query message and it
is an optional parameter in Query Reply message. When being used in
the Query message, it carries the label or stack of labels which are
being followed and queried. When being used in the Query Reply
message, it carries the list of labels which make up the queried
path.
The format for the Query Label TLV is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| Query Label TLV (0x0841)| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Generalized Label TLV 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Generalized Label TLV n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Generalized Label TLV is used to encode labels along the path. Please
refer to [OPTICAL reference] for more information on the Generalized
Label TLV encoding. If the Q2 flag is set, every LSR has to encode
the out-label corresponding to the queried LSP. In the Query Label
TLV, labels are organized as a last-in-fist-out stack (the first
label in TLV is considered the top). They should be encoded in the
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same order as the hops and the merge flags.
7.2. Query Merge Flags TLV
The Query Merge Flags TLV is used to encode the information about
which LSRs along the path the queried LSP is being merged into.
The format for the Query Merge Flags TLV is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| Merge Flags TLV (0x0842) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of merge flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Merge flags | | | ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Query Merge Flags TLV has 4 bytes field to store the number of
merge flags. This number is equal to the number of LSRs which are
traversed by the Query-Reply Message. Each 2 bits in the Merge flags
field represent the merge information for an LSR. The bits are set to
01 if the LSR does not do merge for the queried LSP and are set to 10
otherwise. If the LSR want to hide the merging information, it has to
set the merging flags to 00. The length of the encoding is rounded
up to the next byte. Every LSR which is asked to encode the merging
info into this TLV has to update the Number of merge flags and to set
its corresponding bits accordingly.
7.3. Status code summary
Status Code E Status Data Section Title
No Lsp to query 1 0x0000001a "Query Message Procedures..."
Ambiguous label value 1 0x0000001b "Query Message Procedures..."
Paraschiv, et. al. [Page 16]
Internet Draft draft-ietf-mpls-lsp-query-03.txt August 2001
8. Acknowledgments
The authors would like to acknowledge the careful review and comments
of Jean-Pierre Coupal, Steve Hamilton, Don Fedyk, Gregory Wright and
Adrian Farrel.
9. References
[CR-LDP] Jamoussi et al., "Constraint-Based LSP Setup using LDP",
draft-ietf-mpls-cr-ldp-03.txt, October 1999
[LDP] Andersson et al., "LDP Specification", draft-ietf-mpls-ldp-07.txt,
May 2000.
[RSVP-RR] Berger L., Gan D., Swallow G., Pan P., Tommasi F., Molendini
S., "RSVP Refresh Overhead Reduction Extensions", draft-ietf-rsvp-
refresh-reduct-04.txt.
[CR-LDP] Peter Ashwood-Smith et al., "Improving Topology Data Base
Accuracy with LSP Feedback", draft-ietf-mpls-te-feed-01.txt
Ashwood-Smith P., Berger L., "Generalized MPLS-Signaling Functional
Description" draft-ashwood-generalized-mpls-signaling-00.txt
Paraschiv, et. al. [Page 17]
Internet Draft draft-ietf-mpls-lsp-query-03.txt August 2001
10. Author's Addresses
Peter Ashwood-Smith Antonela Paraschiv
Nortel Networks Corp. Nortel Networks Corp.
P.O. Box 3511 Station C, 600 Technology Park Drive
Ottawa, ON K1Y 4H7 Billerica, MA 01821
Canada USA
Phone: +1 613-763-4534 phone: +1 978-288-6136
petera@nortelnetworks.com antonela@nortelnetworks.com
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Paraschiv, et. al. [Page 18]
